As the economic idea of the environmental protection and low carbon is increasingly popular in the world and rooted in the hearts of people, the requirement of reducing the power consumption of the wireless communication system from the operator is higher and higher. In the wireless communication system, the radio frequency power amplifier (abbreviated as power amplifier) in the base station is one of the core modules of the whole system, and the important technical parameter of the radio frequency power amplifier is the efficiency of the power amplifier. The data analysis shows that, in the whole base station, the energy consumption of the power amplifier part occupies about 60% of the whole energy consumption, thereby raising the efficiency of the power amplifier becomes the most effective means of reducing the power consumption of the base station device and reducing the operation expense (OPEX) of the operator. So, in the face of the fierce market competition of the wireless communication day by day, the high-efficiency radio frequency power amplifier technology has already become one of the competitive focuses of the wireless communication industry.
The Doherty power amplifier is a kind of high-efficiency power amplifier technology that is most extensively employed in the wireless communication system at present, and the Doherty power amplifier is invented by an American electronics engineer, named William H. Doherty, in 1936. But in the following about 30 years, the attention of people has been shifted. Until end of the sixties, along with the development of the communication technology, especially the satellite communication, the efficiency and linear question of the power amplifier is proposed in a new historical occasion again, and the Doherty amplifier is excavated out again, which then is widely applied to the communication and broadcast system in the seventies extensively. At present, the Doherty power amplifier and digital pre-distortion (DPD) technology are applied in combination, which has already become the mainstream frame format of the high-efficiency power amplifier of the base station of the wireless communication system.
The basic idea of the Doherty power amplifier is active load pull, and the principle of the traditional Doherty power amplifier is shown in FIG. 1, which mainly includes driver stage amplifiers (Dr1 . . . Drn in the figure), a power splitter (D in the figure), a carrier amplifier (C in the figure, also called as the main power amplifier), a peak amplifier (P in the figure, also called as the auxiliary power amplifier), a power combiner (Combiner in the figure), etc. Wherein, the carrier power amplifier works in class B or class AB, and the peak power amplifier works in class C. The two bear different input signal power respectively, and the two parts of power amplifiers need possible to be made work in their own saturation areas, thereby guaranteeing the whole power amplifier keep higher efficiency in all of the input signal power range as large as possible, and guaranteeing a certain linearity at the same time.
The Doherty power amplifier mainly includes the following three kinds of working states:
a small-signal area, wherein, when the input signal is relatively small, the peak amplifier is in a shutoff state, and the carrier amplifier works in the AB class, at this moment, the carrier amplifier works in the maximum efficiency matching state;
a load modulation area, wherein, when the input signal increases to a certain extent, the carrier amplifier performs the transition from the amplifier area to the saturation area gradually, and the peak amplifier performs the transition from the cut-off area to the amplifier area gradually, at this moment, the load of both the carrier amplifier and the peak amplifier is not stable, and the load impedance varies with the power variation;
a saturation area, wherein, along with the continuous increasing of the input signal, the carrier amplifier and the peak amplifier all work in the saturation state finally, both the two correspond to the load of 50Ω, and the output power is increased.